Alkali metal ion conductive polymer electrolytes are of considerable interest for use in high energy density batteries, sensors and electrochromic devices. Conventional polymer electrolytes consist of complexes of Li salts with organic polymers having an electron donor atom such as O or N. The most prominent example of conventional polymer electrolytes are the complexes of alkali metal salts, particularly Li salts, with poly(ethylene oxide), (PEO). PEO-based electrolytes have very low conductivities of the order of 10.sup.-8 ohm.sup.-1 .multidot.cm.sup.-1 at room temperature so that they are not practical for normal temperature applications. Therefore, rechargeable Li batteries utilizing PEO-based electrolytes are operated at about 100.degree. C. where the electrolytes attain a practical conductivity of about 10.sup.-3 ohm.sup.-1 .multidot.cm.sup.-1. Conductivities of this magnitude are exhibited at room temperature by nonaqueous liquid electrolytes and are required for the fabrication of electrochemical devices suitable for moderate to high rate applications.
According to the prevailing theory, ionic conduction in polymer electrolytes is facilitated by the large-scale segmental motion of the polymer backbone and primarily occurs in the amorphous regions of the polymer electrolyte. Crystallinity restricts polymer backbone segmental motion and significantly reduces conductivity. Consequently, polymer electrolytes with high conductivity at room temperature have been sought through polymers which have highly flexible backbones and have largely amorphous morphology. Li salt complexes of polymers such as poly[bis-(methoxyethoxyethoxy)phosphazene (reported by Blonsky et al., J. Am. Chem. Soc., 106, 6854 (1984) and poly(ethoxy-ethoxy-ethoxy-vinyl ether) (described by Pantaloni et al., Electrochim. Acta, 34, 635 (1989), prepared on the basis of these principles, have shown room temperature conductivities of around 10.sup.-5 ohm.sup.-1 .multidot.cm.sup.-1.
We have discovered that polymer electrolytes having conductivities greater than 10.sup.-4 ohm.sup.-1 .multidot.cm.sup.-1 at room temperature can be obtained by immobilizing complexes of a low lattice energy Li salt such as LiClO.sub.4, LiBF.sub.4, LiAsF.sub.6 or LiCF.sub.3 SO.sub.3 and a high dielectric constant aprotic organic solvent(s) or mixtures of solvents such as propylene carbonate and ethylene carbonate in poly(vinyl chloride) (PVC). In this manner, ionic conductivity typical of liquid electrolytes can be obtained in a solid polymer electrolyte. This approach of preparing highly conductive solid polymer electrolytes has been successfully demonstrated with the development of electrolytes with conductivities of .about.2.times.10.sup.-3 ohm.sup.-1 .multidot.cm.sup.-1 at room temperature. Using these electrolytes we have fabricated and cycled rechargeable Li and batteries at room temperature. This invention is the subject of this patent application.